Plasma-coated sealing element

ABSTRACT

A method includes using a sealing element to dynamically seal a sealing body in the presence of a lubricant. The sealing element has an elastomeric base body and a plasma coating. The coating includes the elements carbon, oxygen, silicon, and hydrogen. The coating has the following properties at least at the surface: the amount ratio C:Si (at %/at %) is &gt;5, the amount ratio O:Si (at %/at %) is &gt;3, and the surface energy is &lt;50 mN/m. In an embodiment, the coating includes the element fluorine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Entry under 35 U.S.C. § 371 ofInternational Application No. PCT/EP2018/059835, filed on Apr. 18, 2018,and claims priority to European Patent Application No. EP 17169930.9,filed on May 8, 2017. The International Application, which is herebyincorporated by reference herein, was published in German on Nov. 15,2018 as WO 2018/206248 under PCT Article 21(2).

FIELD

The present invention relates to the use of a sealing element fordynamically sealing a sealing body in the presence of a lubricant. Thesealing element can have an elastomeric base body and a plasma coating.The present invention also relates to sealing systems, sealing methods,sealing elements and methods for the production thereof.

BACKGROUND

In the field of sealing technology, moving machine parts in assembliesare sealed with suitable sealing elements (sealing articles). In thecase of dynamic seals, a movement of the sealing body to be sealedrelative to a sealing element takes place. Examples of dynamic sealsinclude mechanical seals, radial shaft sealing rings, labyrinth shaftseals, rod seals, O-rings, and piston rings. The moving interface indynamic seals is referred to as a sealing gap. The sealing elementadjoins a machine part, such as a shaft, piston or rod. The dynamicseals may contain lubricants. These lubricants serve for lubricatingmoving machine components in the assembly (e.g. transmission).

In this case, the lubricant can penetrate into the sealing gap. Sealingelements often consist of polymeric materials, such as thermoplastics orelastomers. The flexibility of such elastomers allows the sealingelements to be adapted to the sealing body during assembly and duringoperation.

In movable sealing systems, considerable forces act on the sealingelements which, because of the relatively low hardness of elastomers,cause sealing elements to wear out as a result of abrasion. Sealingelements therefore often have a limited service life and must bereplaced on a regular basis. In order to improve stability, the hardestpossible elastomers which are generally reinforced with fillers are usedin the prior art. However, this has the disadvantage that although wearof the sealing elements can be reduced, the sealing body is worn out byabrasion at the same time. This effect, which in practice occurs even inthe case of sealing bodies made of steel, is referred to as shaftshrinkage if the counter-rotating partner of the sealing element is ashaft.

In dynamic seals, the lubricant of the assembly to be sealed canpenetrate into the sealing gap. As a result, the lubricants can improvethe tribological properties and thereby reduce the wear. In the case ofdynamic seals with lubricants, a challenge is presented of matching thesealing element, the sealing body and the lubricant to one another suchthat good sealing, good tribological properties and low wear areachieved all at the same time. Practically, it is very difficult or evenimpossible to completely prevent or at least minimize the abrasion ofboth the sealing element and the sealing body in a specific sealingsystem which is exposed to high loads. Sealing systems with lubricantsbehave differently from dry systems.

In order to solve the problem of abrasion, EP 2 291 439 B1 proposes tofurnish elastomeric sealing elements with a plasma coating consistingsubstantially of carbon, oxygen, silicon, hydrogen and optionallyfluorine. The silicon and oxygen contents are relatively high. Thecoating is therefore glass-like and has a relatively high hardness. Thecoated sealing element therefore has a high abrasion resistance at thesurface, while the flexibility of the material desired for sealingapplications is to be maintained in the interior. It is disadvantageous,however, that such hard coatings generally cause a high degree of wearof the sealing body (shaft shrinkage). In practical applications, shaftshrinkage is generally more problematic than wear of the sealingelements since the manufacture and the exchange of machine parts isoften more complex in comparison. Compatibility with various lubricantsis also not always given. Especially at high loads, the stability ofsuch sealing systems is therefore in need of improvement and they areunsuitable for many applications. Moreover, when using very hardcoatings, there is a risk of the sealing element losing its sealingeffect.

Methods of plasma-assisted chemical or physical vapor deposition (CVD orPVD) for providing elastomeric substrates with hard plasma coatingsconsisting almost entirely of carbon are also known in prior art.Because of their hardness and structure, such coatings are referred toas “diamond-like carbon” (DLC). An overview of such methods and productsis given in Martinez-Martinez, De Hosson, 2014, Surface and CoatingTechnology 258, 677-690. However, such coated articles are not suited,or are suited only to a limited extent, for dynamic sealing applicationsbecause in practice relatively strong abrasion and wear of the sealingbodies (shaft shrinkage) is caused due to the high hardness. Suchabrasion of the sealing body can be problematic because it is usually amachine part in practice. The functioning of the machine can be impairedby the abrasion. The exchange of machine parts, such as shafts, isgenerally significantly more complex and expensive than the exchange ofsealing elements, such as sealing rings. The wettability of suchproducts with lubricants is also often inadequate. As a result,tribological properties, wear and abrasion are in need of improvement.Furthermore, there is no indication in literature that these coatingsystems are also suitable for use on sealing bodies since the issue ofobtaining the sealing effect has not been addressed.

The tribological properties of DLC-coated elastomers in dry sealingsystems are described, for example, in Thirumalai, 2016, Surface andCoating Technology 302, 244-254. In this case, significant wear ofvarious coated substrates was observed because of the friction. Dynamicseals with lubricants were not investigated.

DE 10 2012 010 603B4 relates to sealing elements with plasma coatingsfor dynamic seals in the presence of lubricants. When used in lubricatedsealing systems, an unwanted shaft shrinkage is obtained at the sealingbody even though it is significantly reduced in comparison to uncoatedsealing elements. The tribological properties are also still in need ofimprovement. The coatings have surface energies greater than 50 mN/m.Since the surface energy is a measure of wettability, compatibility withmany lubricants is likewise in need of improvement.

The dissertation of Michael Lubwama, “Tribological behaviour of DLC andSi-DLC films deposited on nitrile rubber for handpump piston seals,”2013, Dublin City University, relates to DLC coatings on elastomericnitrile rubber sealing elements comprising only a small amount ofsilicon. The sealing elements are used as dry seals in order to sealwells against leakage of water. Applications with synthetic lubricantsare not described.

Sealing elements and sealing systems remain in need of improvement.Specifically, there is a need for sealing systems configured to overcomethe disadvantages described.

SUMMARY

In an embodiment, the present invention provides a method includingusing a sealing element to dynamically seal a sealing body in thepresence of a lubricant. The sealing element has an elastomeric basebody and a plasma coating. The coating includes the elements carbon,oxygen, silicon, and hydrogen. The coating has the following propertiesat least at the surface: the amount ratio C:Si (at %/at %) is >5, theamount ratio O:Si (at %/at %) is >3, and the surface energy is <50 mN/m.In an embodiment, the coating includes the element fluorine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a schematically shows an exemplary sealing system.

FIG. 1b schematically shows an exemplary sealing system.

FIG. 2 shows the result of the contact angle measurement of a polyglycollubricant on FKM with coating (dashed line) and without coating (solidline), according to an embodiment described in Example 11.

FIG. 3 shows the Stribeck curves of coated FKM (circles) and uncoatedFKM (squares), according to an embodiment described in Example 12.

DETAILED DESCRIPTION

In an embodiment, the present invention provides sealing systems fordynamic seals which overcome the disadvantages described above. In anembodiment, the invention provides sealing systems that showadvantageous properties and especially high stability in the presence ofsynthetic lubricants. The sealing systems exhibit good tribologicalproperties in dynamic sealing applications, especially good frictionalbehavior.

In an embodiment, the present invention provides sealing systems which,in the presence of lubricants, exhibit at most little but preferably noabrasion of the sealing body (shaft shrinkage).

Sealing systems that are stable and efficient over long periods of timeare provided.

In an embodiment, the invention provides efficient and stable sealingsystems for use with polar lubricants, such as polyethers, e.g.polyalkylene glycols, polyesters or water-based lubricants, especiallyat relatively low temperatures, as in devices with oil sump temperaturesbelow 80° C.

In an embodiment, the

objectives are surprisingly achieved by uses, sealing systems, sealingelements and methods according to the claims. Further advantageousembodiments are disclosed in the description.

In an embodiment, the invention provides a sealing element fordynamically sealing a sealing body in the presence of a lubricant, thesealing element having an elastomeric base body and a plasma coating,

-   -   wherein the coating comprises the elements carbon, oxygen,        silicon, hydrogen and optionally fluorine,    -   wherein the coating has the following properties at least at the        surface:    -   the amount ratio (at %/at %) of C:Si is >5    -   the amount ratio (at %/at %) of O:Si is >3, and    -   the surface energy is <50 mN/m.

An embodiment of the invention relates to a sealing system (a seal)having a sealing element which comprises at least one sealing body. Thesealing system is, for example, an assembly, such as a transmission. Thesealing body is usually a machine part. The sealing element and thesealing body form an interface which is referred to as a sealing gap insealing technology. The sealing system is a dynamic seal in which thesealing element and the sealing body move relative to one another whenused as intended. Lubricants are preferably used in this case. Theselubricants can penetrate into the sealing gap during use, whereby thetribological properties are improved. The term “tribology” is thescience of friction, that is to say especially the science ofcalculating and measuring friction coefficients, wear and lubricationbetween interacting bodies and surfaces that are in motion with respectto one another.

In dynamic seals, such sealing systems substantially serve to ensure theinteraction of different machine parts. Such sealing systems should havegood tribological properties and exhibit low wear. In order to improvethese properties, lubricants, such as oils and greases, are used on aregular basis. In addition, the lubricants can also serve to seal thesealing systems against fluids.

The sealing element has an elastomeric base body as a substrate and aplasma coating applied thereto. The coating is preferably applieddirectly to the base body. However, there may also be a furtherintermediate layer, for example in order to improve adhesion. Theelastomeric base body preferably has or consists of an elastomericpolymer. The base body can be completely or partially coated in thiscase. The plasma coating is present at least on the part of the basebody which forms the sealing gap in the sealing system.

The base body is provided with a plasma coating. The plasma coating ispreferably produced by a plasma-assisted chemical vapor deposition(PE-CVD) method. In this case, the base body is placed in a PE-CVDdevice (plasma device) into which volatile, i.e. gaseous or vaporous,precursors (monomers) are introduced for coating. The precursor ischemically and physically altered in the plasma, and reactiveintermediates and polymers which deposit on the surface of the base bodyare produced. Plasma coatings generally form a three-dimensionalcross-linked structure. They are therefore often also referred to asplasma polymeric coatings. It is also possible to produce the coating byplasma-assisted physical vapor deposition (PVD).

The coating contains the elements carbon, oxygen, silicon, hydrogen andoptionally fluorine. This means that these polymer molecules arecomposed of at least these elements. The coating preferably consists ofcarbon, oxygen, silicon, hydrogen and optionally fluorine. In onepreferred embodiment, fluorine is present. In a further embodiment,nitrogen is present, for example in a proportion of up to 10 at % or upto 5 at %. In general, minor, unavoidable impurities of further elementsmay be present, for example in an amount of <5 at %, <2 at % or <1 at %.Such impurities arise, inter alia, when constituents of the base bodytransition into the plasma phase in reactive plasma and are incorporatedor embedded into the coating. Typical impurities are, for example,metals, such as sodium or zinc.

According to an embodiment of the invention, the coatings a contain arelatively large proportion of carbon and only a small proportion ofsilicon. At least at the surface, the coating has an amount ratio (at%/at %) of C:Si of >5 and an amount ratio (at %/at %) of O:Si of >3.

Within the specification, amounts and proportions of the coating arespecified in atomic percent (at %) unless expressly stated otherwise.The amounts at the surface of the coating can be determined by means ofX-ray photoelectron spectroscopy (ESCA, electron spectroscopy forchemical analysis; also referred to as XPS, X-ray photoelectronspectroscopy). This method, which is customary in the prior art,determines the composition at the surface to a depth of a fewnanometers. The composition is preferably measured at the surface in theupper 1 to 20 nm, especially in the upper 2 to 10 nm or, for example, inthe upper 4 or 5 nm. The method allows for detecting all chemicalelements except hydrogen.

In one preferred embodiment, the coating has an overall amount ratio (at%/at %) of C:Si>5 and an amount ratio (at %/at %) of O:Si>3. This meansthat the coating has these amount ratios on average. Preferably, thecoating has such an amount ratio everywhere, or at least in regionswhich make up >80, >90 or >95% of the coating and/or of itscross-section. In one preferred embodiment, the composition of thecoating is substantially homogeneous. Uniform coatings are produced bykeeping the type and concentration of the gaseous precursors constantduring the coating process. This does not rule out a brief pretreatmentwith another process gas for example at the beginning of the process,for example in order to clean and/or activate the surface of the basebody and/or to improve adhesion to the base body at the interface. As isknown to the person skilled in the art, the composition of the surfacemay vary somewhat especially at the interface to the base body becauseat the beginning of the plasma coating production process, a reactionwith the base body and its activated constituents can also take place.

According to an embodiment of the invention, it is also possible for thecoating to have various partial layers with different compositionsand/or for the coating to have a gradient structure. Suchnon-homogeneous composition coatings can be produced by varying the typeand/or concentration of the precursors during plasma coating.

The preferred compositions disclosed below can be adjusted either onlyat the surface of the coating or throughout the coating. According to anembodiment of the invention, it is important to adjust an advantageouscomposition at the surface of the coating where it is in contact withthe lubricant and forms the sealing gap.

In one preferred embodiment, the amount ratio (at %/at %) C:Si is >10or >20, preferably <80 or <70. Preferably, the amount ratio (at %/at %)C:Si is in the range from 5 to 80, preferably from 10 to 70 or from 25to 70.

Preferably, the amount ratio (at %/at %) O:Si is >4 or ≥5.

Preferably, it is <20 or <15. It is especially in the range from 3 to20, preferably from 4 to 15.

Preferably, the amount ratio (at %/at %) C:O is >3, particularlypreferably >4. It is preferably <12, especially <10. The ratio isespecially from 3 to 12, especially from 4 to 10.

In one preferred embodiment, the amount ratio (at %/at %) C:Si is from10 to 80, the ratio O:Si is from 4 to 15, and the ratio C:O is from 3 to12.

In one preferred embodiment, the proportion of Si is from 0.5 at % to 5at %, preferably from 1 at % to 5 at % or from 1 at % to 4 at %.Surprisingly, it was found that even such a small proportion selectivelyincorporated into the polymeric coating can lead to a significantimprovement in properties.

The coatings consist to a significant degree of carbon, preferably at aproportion of at least 50 at %, preferably more than 60 at %, preferablyat a proportion from 50 at % to 95 at %, especially between more than 60at % and 90 at %. The oxygen proportion is preferably from 5 at % to 25at %, especially from 9 at % to 18 at %. The fluorine proportion may beup to 35 at %, especially up to 25 at %. If fluorine is present, theproportion is preferably between 5 at % and 35 at %, especially between7 at % and 25 at %.

In a preferred embodiment, the coating has the following proportions (at%):

Carbon:  50% to 95%, preferably >60% to 90% Oxygen:   5% to 25%,preferably 9% to 18% Silicon: 0.5% to 5%, preferably 1% to 4% Fluorine:  0% to 35%, preferably 0% to 25%

The coatings are characterized overall in that they contain only arelatively small proportion of silicon and oxygen. The coatings therebydiffer from conventional coatings containing either substantially carbonand no silicon (“DLC coatings”) or a relatively high proportion ofsilicon and oxygen of 20-25 at % and which are therefore glass-like(“SiO_(x) coatings”). Coatings of the DLC class are characterized byhigh hardness. They can be produced, for example, from acetylene ormethane as precursor. An overview of the production and properties ofDLC coatings on elastomers is given in Martinez-Martinez (see above).

It was found that the properties of the coatings according to anembodiment of the invention in sealing applications differ significantlyfrom those of carbon-rich coatings without silicon. The coatingsaccording to an embodiment of the invention exhibit, for example, adifferent wettability and surface energy, which is important in thepresence of lubricants. Although the coatings according to an embodimentof the invention have a relatively high carbon proportion, it can beassumed that the incorporation of silicon from precursors in smallproportions in combination with oxygen results in a structuresignificantly different from that of known carbon-rich coatings.

Because of the relatively low proportion of silicon, inter alia, thecoatings also differ significantly from known coatings which have a highproportion of silicon and oxygen. Such coatings are glass-like and havea relatively high hardness. They are described in EP 2 291 439 B1.

According to an embodiment of the invention, the coating is obtainableby a PECVD method in which a volatile, i.e. gaseous or vaporous, siliconprecursor is used. In PECVD methods, the composition of the coating isadjusted by the selection and amounts of gaseous precursors. At leastone precursor containing silicon is used. A compound consisting ofsilicon, carbon and hydrogen is particularly preferably used. This isespecially an alkylsilane, preferably a tetraalkylsilane, particularlypreferably tetramethylsilane (TMS).

In general, preference is given to precursors which contain at leastsilicon, carbon and/or oxygen. In order to achieve a low siliconproportion, a further precursor which contains no silicon and which isespecially a carbon precursor is preferably used according to anembodiment of the invention. In particular used is at least one compoundconsisting of carbon and hydrogen, particularly preferably methane,ethylene or acetylene (ethine, C₂H₂). In particular, a mixture ofacetylene and TMS is used. In order to obtain the required low siliconproportion, the compound which does not contain silicon is usually usedin significant excess, for example at a weight ratio of at least 10:1.The exact concentrations and conditions are adjusted with respect to theparticular compounds, the plasma device, and the desired coatingcomposition.

It is known in the prior art that constituents of the base body can alsobe activated in the reactive plasma. These constituents can be releasedas reactive compounds into the gas phase and merge into the coating.This phenomenon occurs primarily at the beginning of the process whenthe surface of the base body is still uncoated and hence unprotected.Therefore, it is often observed in practice that a plasma coating has asomewhat different composition especially in the boundary region to thesubstrate. However, this is unimportant according to an embodiment ofthe invention as it is crucial for the coating to have the desiredadvantageous composition at the surface.

The coating is applied to an elastomeric base body. The main constituentof the base body is at least one organic polymer which may also be asilicon organic or fluorine polymer. The polymer is an elastomer forminga three-dimensionally cross-linked matrix. The elastomer gives the basebody elasticity and flexibility, which are advantageous during theassembly and intended application of the sealing elements.

Preferred elastomeric base bodies are selected from fluoroelastomers(FKM, FFKM), EPDM (ethylene propylene diene elastomer), nitrilebutadiene elastomers (NBR), hydrogenated nitrile butadiene elastomers(HNBR). Silicones, NR (natural rubber), polyacrylate elastomers (ACM),CR (chloroprene elastomer), HR (isobutene isoprene elastomer), AU(polyester urethane), EU (polyether urethane), MQ (methylene siliconeelastomer), VMQ (vinyl methyl silicone elastomer), PMQ (phenyl-methylsilicone elastomer), FMQ (fluoro-methyl silicone elastomer), FERM(tetrafluoroethylene propylene elastomer), or mixtures of suchelastomers. In one preferred embodiment of the invention, theelastomeric base body comprises at least one polymer selected fromfluoroelastomers (FKM, FFKM), EPDM (ethylene propylene diene elastomer),nitrile butadiene elastomers (NBR) and hydrogenated nitrile butadieneelastomers (HNBR).

The base body preferably consists of at least 40 wt. %, at least 50 wt.% or at least 60 wt. % of at least one such polymer. In this case, thebase body may contain customary additives, such as fillers, which may beorganic or inorganic, dyes, stabilizers or plasticizers. Elastomers forsealing applications often contain fillers in order to improve hardnessand stability.

In one preferred embodiment, the elastomeric base body is afluoroelastomer. This generally refers to organic polymers containingfluorine. Preferably, the fluoroelastomer is a fluoro rubber (FKM) or aperfluoro rubber (FFKM). Fluoro rubbers (FKM) are produced bypolymerization using vinylidene (di)fluoride (VDF), in which case othermonomers, such as hexafluoropropylene (HFP) or tetrafluoroethylene(TFE), can additionally be used. Suitable FKMs are, for example,copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP)and terpolymers of VDF, HFP and tetrafluoroethylene (TFE). Particularlypreferred are FKMs according to the definition of DIN ISO 1629 or ASTMD1418. Further suitable fluorinated elastomers aretetrafluoroethylene/propylene rubbers (FEPM) and fluorinated siliconerubber. In one preferred embodiment, the fluoroelastomer iscross-linked. Such cross-linked fluoroelastomers and their productionare described, for example, in EP 1 953 190 B1.

In one preferred embodiment, the fluoroelastomer consists substantiallyof carbon and fluorine. In this case, it is possible for a smallproportion to also consist of other elements, for example becauseadditives which do not consist of fluorine and carbon, such ascross-linkers, are used in the polymerization. In preferred embodiments,the fluoroelastomer therefore consists of more than 90 wt. %, of morethan 95 wt. % or of more than 98 wt. % of carbon and fluorine.

Preferably, the base body and/or the sealing element is/are a sealingring, a rotary seal or a cassette seal. The sealing ring is especially ashaft sealing ring. Preferred sealing elements for dynamic seals are,for example, mechanical seals, radial shaft sealing rings, labyrinthshaft seals, rod seals, O-rings or piston rings. Such sealing elementsseal machine housings against the surroundings at exiting elements, suchas shafts or push rods. In a particularly preferred embodiment, thesealing element is a radial shaft sealing ring (RWDR). Radial shaftsealing rings are especially those defined in DIN3760. In one preferredembodiment, the sealing ring is an axial shaft sealing ring. In dynamicsealing applications, such sealing rings are highly exposed to strongforces which in combination with lubricants can lead to high wear of thesealing elements and to high shaft shrinkage.

The elastomeric base body is at least partially provided with a coating.In one embodiment of the invention, the elastomeric base body iscompletely provided with the coating. In a preferred embodiment, onlyportions of the base body are coated. The coated portions can make up,for example, 5 to 90%, especially 10 to 60%, of the surface of the basebody. The decisive factor in this case is that the sealing gap, thecontact surface to the sealing body and/or preferably also the adjoiningregions of the base body are coated.

The coating preferably has a layer thickness in the nanometer range. Forexample, the layer thickness is between 5 and 3000 nm, especiallybetween 100 and 1500 nm.

The coating has a relatively low surface energy of <50 mN/m, preferably<45 mN/m or <40 mN/m. The surface energy is preferably >20 mN/m,especially >25 mN/m or >30 mN/m. It is preferred for the surface energyto be in the range of 20 to 50 mN/m, especially in the range of 25 to 45mN/m or 30 to 40 mN/m.

The surface energy (surface tension) is the total potential energy ofthe molecules located at or near the surface of a solid. In a solid,attractive forces act between the molecules which hold the solidtogether. These forces do not act on molecules at the surface from allsides but only from the inside. This results in a tensile force actinginwardly on molecules located at the surface. Work is therefore requiredto bring a molecule from the inside to the surface, and molecules at thesurface have a corresponding potential energy. The surface energy is acharacteristic value for the interaction between the surface of acondensed phase (solid or liquid) and its environment. It is specifiedin mN/m. The surface energy is a criterion for the wettability of amaterial. It can be increased by various plasma methods. The surfaceenergies of solids range from less than 20 mN/m (e.g. PTFE) to severalthousand mN/m (metals, diamond).

The surface energy of a coating can be influenced in a targeted mannerby various measures during the production in the plasma. For example,the surface energy is influenced by the change in the proportion ofoxygen-containing gases, the selected total gas quantity, the power orthe reactivation of the surface, for example by varying the constituentsin the plasma. A suitable way to increase the surface energy is to useprocess gases containing polar atoms, such as nitrogen or oxygen.According to an embodiment of the invention, the relatively low surfaceenergy of <50 mN/m can be obtained, for example, if the coating has arelatively small proportion of silicon, a relatively high proportion ofcarbon and a relatively low proportion of oxygen.

The surface energy is measured indirectly via the contact angle which isformed between the solid and a liquid having a known surface tension atthe phase boundary. Young's equation describes the relationship betweenthe contact angle, the surface tension of the liquid, the interfacialtension between the two phases, and the surface energy of the solid.According to an embodiment of the invention, the surface energy ismeasured according to the static contact angle measurement method withwater and diiodomethane as polar or non-polar liquid. The contact anglemeasurements are evaluated according to the equation of Owens and Wendt.DIN 55660-2 (December 2011; Paints and varnishes—Wettability—Part 2:Determination of the free surface energy of solid surfaces by measuringthe contact angle) is particularly suitable for the determination.

The sealing element adjoins a sealing body. The sealing body isespecially a machine part customary for sealing applications, forexample a shaft. Such sealing bodies are often comprised of metal, forexample steel. It is known in the field of sealing technology that shaftshrinkage, i.e. the abrasion of the sealing body, which can lead toleakage of the entire system or destruction of the sealing body,constitutes a great practical problem. Abrasion is caused by the sealingelements generally also having a relatively high hardness in order notto be abraded too much or destroyed themselves. In the prior art, thehardness of elastomeric sealing elements is regularly increased byincorporating fillers. The term “leakage” refers especially to theunwanted escape of the lubricant from the sealing system.

The use according to an embodiment of the invention takes place in thepresence of a lubricant. Materials which reduce friction or wear in asealing system are referred to as lubricants. In this case, the sealingelement is wetted by the lubricant in the region of the sealing gap,wherein wetting takes place especially on the so-called oil side. Thelubricant serves primarily to reduce friction and wear and thereby tolengthen the service life of the sealing system.

Lubricants are liquid or lubricating under operating conditions. Theyare generally organic substances or mixtures of substances. Customarylubricants are, for example, greases or oils. The lubricant ispreferably selected from organic lubricating oils, especially syntheticlubricating oils. Because of the low surface energy, the sealing elementaccording to an embodiment of the invention is suitable for sealing inthe presence of both polar and oleophilic lubricants. The lubricant maybe generally polar or oleophilic (miscible with oils). Suitablelubricants contain or are, for example, polyethers, polyesters,water-based lubricants, silicone oils or polyalphaolefins. Water-basedlubricants contain water and organic compounds, such as polyethers,polyesters and/or surfactants, preferably in a proportion of 5 wt. % ormore. They are described, for example, in EP 2 473 587 B1.

The use of polar lubricating oils is particularly preferred. Preferably,the polarity is higher than that of mineral oils. The lubricant is, inparticular, preferably hydrophilic, i.e. miscible or partially misciblewith water. Polar lubricating oils have polar groups, especiallyoxygen-containing groups, such as hydroxyl groups, ether groups or estergroups. The lubricant is preferably a polyether, polyester or a mixturethereof.

The lubricants polyalkylene glycols are particularly preferred. They areproduced by polymerization of alkylene oxide units, usually ethyleneoxide or propylene oxide units or combinations thereof, initiated by theattachment to an alcohol. In this case, the proportion of ethylene oxidedetermines the solubility in water. A polypropylene glycol isparticularly preferably used. Various polyalkylene glycols arecommercially available under the brand name “polyglycol.” Polyalkyleneglycols have high temperature resistances and a high potential forminimizing friction in tooth systems. Suitable polyglycol oils arecommercially available, for example under the brand name Klübersynth GH6, or Klübersynth UH1 6-460, manufactured by Klüber Lubrication,Germany. Polar lubricating oils, especially polyalkylene glycols, havebeen found to be particularly compatible with the sealing systemsaccording to an embodiment of the invention.

In a preferred embodiment, the contact angle of the coating to thelubricant is less than 50°, less than 40° or less than 30°, preferablyfrom 10° to less than 50°, still more preferably between 15° and 30°. Atsuch relatively low contact angles, the coating can be wetted well withthe lubricant. It has been found that polar lubricating oils andespecially polyalkylene glycols have such contact angles with thesealing elements according to an embodiment of the invention, whichresults in an efficient, wear-resistant sealing system. The contactangle is preferably determined at room temperature in the equilibriumstate pursuant to DIN 55660-2 (December 2011).

The lubricants have a surface tension of 10-70 mN/m, preferably 15-60mN/m or 20-40 mN/m. Determination of the surface tension by the hangingdrop method pursuant to DIN 55660-3 (December 2011).

The system according to an embodiment of the invention is particularlysuitable when using lubricants that have a relatively high viscosity. Ina preferred embodiment, the lubricant therefore has a kinematicviscosity of >150 mm²/s, preferably 250 mm²/s or >400 mm²/s. Thekinematic viscosity is preferably measured at 40° C. according to ISO3104/ASTM D445.

Use preferably takes place at an oil sump temperature <80° C.,especially <60° C. or <40° C. This refers to the temperature at whichthe oil in the overall device is merged and stored at the lowest point(oil pan, oil sump). In the dynamic sealing system itself, significantlyhigher temperatures caused by the frictional heat of the components canbe present locally.

Use with such high-viscosity lubricants and/or at relatively lowtemperatures <80° C. is particularly advantageous. According to anembodiment of the invention, it was found that especially under suchconditions, especially when using synthetic hydrophilic oils, such aspolyalkylene glycols, a particularly stable sealing system is obtainedwhich is extremely low in wear. This applies especially in combinationwith sealing elements based on fluoroelastomers. For such sealingsystems, it was found that shaft shrinkage can not only be reduced buteven be completely prevented. This is particularly advantageous since,under comparable conditions, relatively strong wear of the sealingelement and/or a relatively strong shaft shrinkage of the sealing bodyis generally observed in the prior art.

According to an embodiment of the invention, it was surprisingly foundthat the sealing element has a particularly advantageous combination ofproperties in a dynamic sealing system. In the prior art, it isgenerally assumed that sealing elements for dynamic sealing applicationsmust be relatively hard in order to prevent damage to the sealingelement by abrasion. It was thus proposed in EP 2 291 439 B1, forexample, to provide sealing elements with glass-like coatings having ahigh silicon and oxygen proportion. Moreover, hard coatings with a highcarbon proportion (DLC) have been proposed in the prior art. However,the disadvantage of such coatings is that, although abrasion of thesealing element can be reduced in practice, the sealing body itself isimpaired by abrasion instead. An undesired shaft shrinkage at thesealing body is observed in shaft applications as a result.

The sealing system according to an embodiment of the invention hasexcellent tribological properties. At the same time, abrasion of thesealing body can be greatly reduced and often even completely prevented.The sealing system is particularly suitable for dynamic sealingapplications in the presence of synthetic lubricants. In the case ofdynamic seals of shafts, shaft shrinkage can thus be largely or evencompletely avoided.

The invention also relates to a sealing system (a seal) comprising thesealing element, a sealing body, an intermediate dynamic sealing gap andoptionally a lubricant. The sealing system is preferably a dynamic seal.

FIG. 1 schematically and by way of example shows sealing systems 1 a, 1b composed of a sealing element 2 and a sealing body 3, which form asealing gap 4, and a lubricant 5. On the left side, a conventionalsystem 1 a is shown in which the lubricant 5 does not completely fillthe sealing gap 4 because wettability is insufficient. With the coatingaccording to an embodiment of the invention, a sealing system 1 b can beobtained, as shown on the right-hand side, in which the sealing gap 4 iscompletely filled with lubricant 5, i.e. in which the sealing element 2and the sealing body 3 are completely wetted in the sealing gap 4.

The invention also relates to a device comprising a system to be sealedwhich contains the dynamic sealing system (the seal). In a preferredembodiment, the device is a transmission, a pump, a motor or a motorvehicle.

The invention also relates to a method for dynamically sealing a sealingbody with a dynamic sealing system according to an embodiment of theinvention, wherein the sealing body and the sealing element aredynamically moved relative to one another.

With the method according to an embodiment of the invention, a sealingsystem comprising the sealing body, the sealing element and thelubricant is provided. The sealing body and the sealing element aremoved relative to one another. It was observed in this respect that thesealing system is stable over longer periods of time. In this case, itis not disadvantageous if slight abrasion of the sealing element occursin the initial phase. A system is obtained which can be operated stablyover a long period of time. It was found, for example, that slightabrasion of the sealing element may take place within less than 96hours, while in a subsequent, longer phase of up to 1000 hours, there isno further significant abrasion. It was observed, moreover, that no wearof the shaft as a sealing body, i.e. no shaft shrinkage, was observedduring the 1000-hour operation. The effect was particularly pronouncedin the case of highly viscous lubricants and relatively lowtemperatures. Overall, a system is provided which stabilizes withincreasing operating time and has permanently good tribologicalproperties.

The invention also relates to a sealing element for dynamically sealinga sealing body in the presence of a lubricant, wherein the sealingelement has an elastomeric base body made of a fluoroelastomer and aplasma coating,

-   -   wherein the coating comprises the elements carbon, oxygen,        silicon, hydrogen and optionally fluorine,    -   wherein the coating has the following properties at least at the        surface:    -   the amount ratio (at %/at %) of C:Si is >5    -   the amount ratio (at %/at %) of O:Si is >3, and    -   the surface energy is <50 mN/m.

The sealing element can be further configured as generally describedabove. The sealing element having a base body made of a fluoroelastomerexhibits particularly advantageous properties in the system according toan embodiment of the invention, especially in combination with polarlubricants, such as polyalkylene glycols.

The invention also relates to a method for producing a sealing elementaccording to an embodiment of the invention by plasma-assisted,preferably chemical, vapor deposition, comprising the steps of:

(a) introducing the elastomeric base body into the plasma device,

(b) introducing at least one gaseous silicon precursor into the device,and

(c) coating the base body in the device.

Plasma-assisted chemical vapor deposition is generally a process inwhich gaseous precursors, also referred to as monomers, excited by aplasma, deposit on a substrate as a cross-linked layer. The monomers inthe gas phase are excited or fragmented, for example, by bombardmentwith electrons and/or high-energy ions. This produces free-radical orionic molecular fragments which react with one another in the gas phaseand are deposited on the surface of the substrate. The electricaldischarge of the plasma and its intensive ion and electron bombardmentcontinuously acts on the layer thus deposited so that further reactionsare triggered and cross-linking of the deposited molecules is achieved.The plasma is preferably a low-pressure plasma, but an atmosphericpressure plasma may also be used. The coating of elastomers in plasma isknown in the prior art and is disclosed, for example, in DE 10 2005 025253 A1. Reference is hereby expressly made to the method disclosedtherein.

According to an embodiment of the invention, the base body can beintroduced initially in step (a) and the precursor(s) can then be addedin step (b), or vice versa. The silicon precursor and optionally thefurther precursors are activated in the plasma. Actual polymerizationcan take place in the gas phase and/or in the coating. In step (c), theintermediates deposit on the base body. Methods for the production ofcarbon-containing coatings by means of plasma-assisted chemical orphysical vapor deposition on elastomeric base bodies are generally knownin the prior art and are described, for example, in EP 2291439 B1,Lubwama, 2003, or Martinez-Martinez and De Hosson, 2014 (seerespectively above).

The uses, sealing elements, sealing systems, devices and methodsaccording to an embodiment of the invention achieve the objectunderlying the invention. Dynamic sealing systems are provided whichshow a combination of advantageous properties. The sealing elements andsealing systems exhibit excellent tribological properties and especiallya very good frictional behavior. They are, moreover, highly stable.Especially, there is at best little abrasion but often no abrasion atall of the sealing bodies. In this way, it is possible to, for example,completely prevent shaft shrinkage on the sealing body in practice.According to an embodiment of the invention, stable systems are providedwhich are stable over long periods of time, possibly after initialself-stabilization by slight abrasion of the sealing elements. This ishighly advantageous for a plurality of practical applications, such asin motors, transmissions or pumps, where the overall service lifedepends on the wear of the individual parts.

FIG. 1 schematically and by way of example shows a sealing systemcomposed of a sealing element, sealing body and lubricant.

FIG. 2 shows the result of the contact angle measurement of a polyglycollubricant on FKM with coating (dashed line) and without coating (solidline), as described in Example 11.

FIG. 3 shows the Stribeck curves of coated FKM (circles) and uncoatedFKM (squares), as described in Example 12.

Examples 1 Through 9 Production and Characterization of Coatings

Various elastomers (see Table 1) are provided with a coating in aplasma-assisted chemical vapor deposition process. For this purpose, alow-pressure plasma system is used for an asymmetric, capacitivelycoupled radio-frequency discharge. The elastomeric bodies (substrates)are positioned in contact with the electrode. In this process, acetyleneand optionally an oxygen-free alkylsilane compound are used as thecarbon source and essential layer-forming precursor. The addition offurther reactive gases, for example oxygen, argon, nitrogen, is alsoconceivable. These gases are put into the plasma state at processpressures of a few pascals through excitation with electromagneticradiation, for example at radio frequency. The molecules are cleaved andcondense on the surface of the base body as a carbon-rich layer when thealkylsilane having a low silicon proportion is used. For better bondingof the layer, the elastomers are first activated in a non-layer-formingplasma, for example composed of argon and/or oxygen. In this case,fragments of the substrate can transition from the surface into theplasma phase and be incorporated into the coating. The essential coatingsteps are listed in Table 2 by way of example. Layer 4 is an exceptionto the preceding explanation. In deviation thereto, these layers are notdeposited in contact with the electrode and serve as a comparison topatent EP 2 291 439 B1.

TABLE 1 Sealing materials used Cross-linking Designation Polymermechanism Main filler FKM I Fluorocarbon rubber Bisphenolic Mineralfillers EPDM I Ethylene propylene Peroxidic Soot diene rubber NBR INitrile butyl rubber Sulfur Mineral fillers

TABLE 2 Process parameters of coating processes Layer 1 Layer LayerLayer 4 Process parameters (Comparative) 2 3 (Comparative) RF power [W]400 300 300 300 Acetylene mass flow 100 350 350 [sccm, N₂ calibrated]TMS mass flow [sccm, 15 25 N₂ calibrated] HMDSO mass flow 120 [sccm, N₂calibrated] O₂ mass flow [sccm, 50 50 120 N₂ calibrated]

The coatings deposited in this way are characterized by means of X-rayphotoelectron spectroscopy with regard to chemical composition (in theinterface to air). In this case, however, the method only determines thelayer chemistry of the uppermost nanometers and definitely not thecomposition of the entire coating. All samples were purified withethanol prior to the measurement. The measured spectra are corrected tothe C 1 s peak at 285.0 eV.

TABLE 3 Chemical composition of various surfaces Si F O C Other ExampleSubstrate [at %] [at %] [at %] [at %] [at %] O/Si C/Si C/O 1 (V) FKM I1.9 48.6 5.1 44.4 2.7 23.4 8.7 1a (V) FKM I with layer 1 19.1 11.6 68.21.3 5.9 2 FKM I with layer 2 2.3 10 14.5 73.3 6.3 31.9 5.1 3 FKM I withlayer 3 1.0 21.2 11.7 65.8 0.4 11.7 65.8 5.6 4 (V) FKM I with layer 416.7 10.5 35.5 35.2 2.1 2.1 2.1 0.99 5 (V) EPDM I 3.3 6.6 90.1 2 27.313.7 6 EPDM I with layer 2 3.3 16.2 80.7 4.9 24.5 5 7 (V) NBR I 2.6 6.588.2 2.7 2.5 33.9 13.6 8 NBR I with layer 2 2.0 10.4 87.6 5.2 43.8 8.4 9(V) Stainless steel with 1.4 17.4 79.9 1.3 12.4 57.1 4.6 layer 2

The results are summarized in Table 3. Examples 2, 3, 6 and 8 areaccording to an embodiment of the invention. Examples 1, 5 and 7(without coating), 1a (without Si precursor), 4 (with Si—O-rich coating)and 9 (on steel) marked with (V) are comparative examples. Example 4with layer 4 corresponds to the layers described in EP 2 291 439 B1since the binding energy of the Si 2p signal measured by means of XPS isshifted by about 1 eV to higher binding energies in comparison totrimethylsiloxy-terminated PDMS. The low content of Si in the uncoatedComparative Examples 1, 5 and 7 can be explained by the fact that theelastomers have additives, such as silicones or silica fillers. Thecomparison of the properties shows that the structure of the surfacescoated according to an embodiment of the invention is very different andthat the advantageous effects with regard to tribological properties andshaft shrinkage are achieved only in case of the plasma coatingsaccording to an embodiment of the invention (see examples below).

Example 10 Determination of Surface Energies and Contact Angles

Contact angle measurements are carried out on the lying drop in order todetermine the surface energies. With the exception of the conditionedatmosphere, the procedure is carried out analogously to the DIN 55660-2standard from December 2011. The measurements are carried out at 23-26°C. Water and diiodomethane are used as measuring liquids. The surfaceenergy is calculated according to the Owens-Wendt method based on thecontact angles resulting from the measurement. The total surface energyis composed of the polar and the disperse parts.

The contact angle measurements are performed one day, 7 and 30 daysafter the coating process. All surfaces were cleaned with ethanol priorto the measurement. Since the base body material is a multi-componentsystem whose individual components tend to migrate to some extent, themeasured values of the contact angles vary by up to 10° due to thematerial. The results are summarized in Table 4. Overall, themeasurements show that the surface energies are relatively low so thatthe coatings can be wetted relatively well.

TABLE 4 Surface energies (in mN/m) of carbon-rich coatings on differentelastomers. After 1 day After 7 days After 30 days Example Product σ_(p)σ_(d) σ_(tot) σ_(p) σ_(d) σ_(tot) σ_(p) σ_(d) σ_(tot) 1 (V) FKM I 0.819.4 22.2 1.3 23.9 25.2 2.0 22.2 24.2 2 FKM I with layer 2 4.4 36.4 40.82.7 29.7 32.4 2.5 28.4 30.9 5 (V) EPDM I 0.1 29.7 29.8 1.3 24.3 25.6 0.428.0 28.4 6 EPDM I with layer 2 5.0 34.0 39.0 0.0 41.1 41.1 0.1 36.636.7 7 (V) NBR I 0.5 42.5 43.0 0.2 37.5 37.7 0.1 37.3 37.4 8 NBR I withlayer 2 0.3 40.0 40.3 1.4 39.6 41.0 0.1 41 41.1

The contact angle to a commercially available polyalkylene glycol oil ofISO viscosity class 460 (of the brand Klübersynth UH1 6-460; KlüberLubrication, Germany) is measured on layer-2-coated and uncoated FKM I.FIG. 2 shows the result of the contact angle measurement on FKM withcoating (dashed line) and without coating (solid line). As a result ofthe coating, wetting is significantly improved and the contact angle inequilibrium is reduced by about two thirds from about 68° to about 22%.The coatings are therefore particularly suitable in combination withpolyalkylene glycol as lubricant.

Example 11 Frictional Behavior Without Lubricant

In order to characterize the frictional reduction of the coatings,coated and uncoated specimens are moved over a stainless-steel plate(R_(a)=1.062 μm) and the necessary force is recorded. For this purpose,three specimens are inserted into a special receptacle which allows acontact surface per specimen of approximately 6.5 mm² to thecounter-rotating partner. The receptacle is placed with the specimensdown onto the counter-rotating partner and weighted down with a mass of1 kg. The counter-rotating partner is then moved at a speed of 150mm/min and the force which has to be exerted in order to hold thereceptacle in place is measured. The measurement is performed threetimes in succession; the mean values are summarized in Table 5. Theresults show that the frictional behavior of the elastomers issignificantly improved by the coatings.

TABLE 5 Frictional forces of various surfaces From Ex. Substrate Force[N] 1 (V) FKM I 12.4 2 FKM I with 2.3 layer 2 5 (V) EPDM I 10.9 6 EPDM2.4 with layer 2 7 (V) NBR I 11.1 8 NBR I with 2.5 layer 2

Friction measurements are carried out analogously to the precedingdescription. However, a polished stainless-steel surface is used as thecounter-rotating partner.

TABLE 6 Frictional forces of various coatings From Ex. Substrate Force[N] 1 (V) FKM I 16.1 1a (V) FKM I with layer 1 4.0 2 FKM I with layer 22.2 3 FKM I with layer 3 2.3 4 (V) FKM I with layer 4 9.5

The results are shown in Table 6. They show that the frictional behaviorof the coated elastomers (Examples 2, 3) according to an embodiment ofthe invention is significantly better than in elastomers with coatingscomprising no silicon (Example 1a) or coatings with high Si—O proportion(Example 4).

Example 12 Frictional Behavior with Lubricant

In order to describe the properties of the lubricated sealing system,comparative tests are carried out on a ring-on-disk test stand (see alsoM. Sommer, W. Haas: “A new approach on grease tribology in sealingtechnology: Influence of the thickener particles,” TribologyInternational, volume 103, November 2016, pages 574-583). For thispurpose, specimens of FKM I are used and tested in comparison inuncoated and layer-2-coated condition (pursuant to Examples 1 and 2). Apolyalkylene glycol oil of ISO viscosity class 460 (Klübersynth UH16-460) is used as lubricant. The test setup is tempered to 60° C. FIG. 3shows the results with coated FKM (circles) and uncoated FKM (squares).A significant reduction in friction due to the coating is also clearlyobserved in the lubricated sealing system. The effect of the coatingbecomes clear especially in the front region of the curves where mixedfriction, solid-state friction and boundary friction occur. A visualinspection of the specimens after the examinations shows minimal wear inthe uncoated specimens. No wear can be detected by visual methods in thecoated specimens.

Example 13 Determination of Abrasion with Sealing Rings and Lubricant inthe Short-Time Component Test

Radial shaft sealing rings (RWDR) consisting of a metal insert which issheathed with fluoroelastomer FKM I are provided with layer 2 asdescribed in Example 2. In a typical short-term test, these componentsare examined for their application properties. Uncoated components arealso tested for comparison. In this short-term test, a steel shaft(90MnCrV8, hardness 55-60 HRC R_(z)=1-5 μm, non-spinning) rotates in thesealing ring at 3000 rpm for 96 hours (p=0.3 bar). A polyalkylene glycoloil of ISO viscosity class 460 (Klübersynth UH1 6-460) at 45° C. oilsump temperature is used as lubricant. The running track width, which isa measure of the sealing edge's wear, is 0.2 to 0.4 mm for both variantsafter the end of the tests. However, the wear of the counter-rotatingpartner, the so-called shaft shrinkage, can be identified as asignificant difference. It is between 7 and 35 pm in the uncoatedcomponents. No shaft shrinkage can be measured in the coated components.All measurements are measured by light microscopy. No leakage wasdetected in any of the sealing systems.

In a further test series, radial shaft sealing rings (RWDR of rubber FKMI) are provided with layers 1 to 4 and characterized in the 96-hour testdescribed. The lubricant used is again a polyalkylene glycol oil of ISOviscosity class 460, this time at an oil sump temperature of 80° C. Theresults are summarized in Table 7.

TABLE 7 Surface energies and wear of differently coated RWDR after96-hour component test Surface Running Shaft energy track widthshrinkage Coating [mN/m] [mm] [μm] Layer 1 44.0 0.39-0.43 4.25 Layer 233.6 0.22-0.28 0 Layer 3 38.5 0.19-0.28 0 Layer 4 49.2 0.39-0.49 5.89

The results show that, in the sealing systems according to an embodimentof the invention, shaft shrinkage of the sealing body can not only bereduced but even be completely prevented. In contrast, the comparativetests with the carbon-rich layer 1 having no silicon and with layer 4(Si—O-rich) show a distinct shaft shrinkage, i.e. wear of the steelsealing body. No leakage was detected in any of the sealing systems.

Example 14 Determination of Abrasion with Sealing Rings and Lubricant inthe Siemens Flender Test

RWDR made of FKM I (75 FKM 585) are provided with a layer 2 as describedin Example 2. Comparative tests are carried out with coated and uncoatedcomponents according to the protocol for the dynamic Siemens Flendertest [FB 73 11 008 (status as per Jul. 30, 2015: Static and dynamic oilcompatibility tests with Freudenberg shaft seals for release for use inFLENDER transmissions, Tables T 7300https://cache.industry.siemens.com/dl/files/658/44231658/att_861254/v1/DE_5-2_RWDR-_und_O-Ringtest_Rev06_2015-07-30.pdf).A polyalkylene glycol oil of ISO viscosity class 460 (Klübersynth UH16-460) at 110° C. is used as lubricant.

After completion of the test series, the wear of the sealing edge foruncoated rings of 0.2 to 0.4 mm is in the same range as the wear of thesealing edge for coated rings of 0.1 to 0.3 mm. Shaft shrinkage in thetribological system with uncoated FKM ring is 30-40 μm. However, in thetribological system with coated rings, no shaft shrinkage can bedetected. Leakage was also not detected in any of the sealing systems.

Example 15 Determination of Abrasion with Lubricated Sealing Rings in aLong-Term Test

RWDR made of FKM I are provided with a layer 2 as described in Example2. The coated surfaces of a test series are additionally provided with agrease prior to testing. Comparative tests are now carried out withlubricated and unlubricated components (shaft: C45R, Rz—1-5 μm,non-spinning; test parameters: t=240 h, T_(lubricant)=70° C., p=0.25bar). In this test, a steel shaft rotates in the sealing ring for atotal of 240 h, alternately 20 h at 2000 revolutions per minute and 4 hat rest. A polyglycol oil of ISO viscosity class 220 at 70° C. oil sumptemperature is used as lubricant.

After completion of the test series, the running track width for bothlubricated and unlubricated seals is 0.1 to 0.2 mm. In all tribologicalsystems (with lubricated or unlubricated rings), no shaft shrinkage canbe detected again. This means that the good tribological properties ofthe sealing rings coated according to an embodiment of the invention areretained even with the additional use of lubricating greases. Asignificant shaft shrinkage occurs when using uncoated but greased RWDR.No leakage was detected in any of the sealing systems.

Disclosed is a method of use of a sealing element for dynamicallysealing a sealing body in the presence of a lubricant. The sealingelement has an elastomer main part and a plasma coating, and the coatinghas the elements carbon, oxygen, silicon, hydrogen, and optionallyfluorine. The coating has at least the following properties on thesurface: the material quantity ratio (at %/at %) of C:Si is >5, thematerial quantity ratio (at %/at %) of O:Si is >3, and the surfaceenergy is <50 mN/m. The invention also relates to sealing systems,sealing methods, sealing elements, and methods for producing same.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Itwill be understood that changes and modifications may be made by thoseof ordinary skill within the scope of the following claims. Inparticular, the present invention covers further embodiments with anycombination of features from different embodiments described above andbelow. Additionally, statements made herein characterizing the inventionrefer to an embodiment of the invention and not necessarily allembodiments.

The terms used in the claims should be construed to have the broadestreasonable interpretation consistent with the foregoing description. Forexample, the use of the article “a” or “the” in introducing an elementshould not be interpreted as being exclusive of a plurality of elements.Likewise, the recitation of “or” should be interpreted as beinginclusive, such that the recitation of “A or B” is not exclusive of “Aand B,” unless it is clear from the context or the foregoing descriptionthat only one of A and B is intended. Further, the recitation of “atleast one of A, B and C” should be interpreted as one or more of a groupof elements consisting of A, B and C, and should not be interpreted asrequiring at least one of each of the listed elements A, B and C,regardless of whether A, B and C are related as categories or otherwise.Moreover, the recitation of “A, B and/or C” or “at least one of A, B orC” should be interpreted as including any singular entity from thelisted elements, e.g., A, any subset from the listed elements, e.g., Aand B, or the entire list of elements A, B and C.

The invention claimed is:
 1. A method comprising: using a sealingelement to dynamically seal a sealing body in the presence of alubricant, the sealing element having an elastomeric base body and aplasma coating, wherein the coating comprises the elements carbon,oxygen, silicon, hydrogen, wherein the coating has the followingproperties at least at the surface: the amount ratio C:Si (at %/at %)is >5 the amount ratio O:Si (at %/at %) is >3, and the surface energy is<50 mN/m.
 2. The method according to claim 1, wherein the proportion ofSi is from 0.5 at % to 5 at % at least at the surface of the coating,and/or wherein the proportion of C is >60 at % at least at the surfaceof the coating.
 3. The method according to claim 1, wherein the amountratio C:O is >3 (at %/at %) at least at the surface of the coating. 4.The method according to claim 1, wherein the amount ratio (at %/at %) ofC:Si at least at the surface of the coating is from 10 to 80, the ratioO:Si is from 4 to 15 (at %/at %) and the ratio C:O is from 3 to 12 (at%/at %).
 5. The method according to claim 1, wherein the coating isobtainable in a plasma coating process in which a gaseous siliconprecursor is used.
 6. The method according to claim 1, wherein thecoating has the following proportions (in at %) at least at the surface:Carbon:  50% to 95% Oxygen:   5% to 25% Silicon: 0.5% to 5% Fluorine:  0% to 35%


7. The method according to claim 1, wherein the elastomeric base body isa fluoroelastomer.
 8. The method according to claim 1, wherein thecontact angle of the coating relative to the lubricant is from 10° to50°.
 9. The method according to claim 1, wherein the lubricant has akinematic viscosity of >200 mm²/s measured at 40° C., and/or wherein thelubricant is a polyether, especially a polyalkylene glycol, or apolyester, or a mixture thereof.
 10. The method according to claim 1,wherein the use is carried out at an oil sump temperature <80° C. 11.The method according to claim 1, wherein the sealing element and/or thebase body is a sealing ring.
 12. A sealing system comprising a sealingelement, a sealing body, and an intermediate dynamic sealing gap,wherein the sealing element has an elastomeric base body and a plasmacoating, wherein the coating comprises the elements carbon, oxygen,silicon, hydrogen, wherein the coating has the following properties atleast at the surface: the amount ratio C:Si (at %/at %) is >5 the amountratio O:Si (at %/at %) is >3, and the surface energy is <50 mN/m.
 13. Adevice comprising a sealing system according to claim 12, especially inform of a transmission, a pump, a motor, or a motor vehicle.
 14. Asealing element for dynamically sealing a sealing body in the presenceof a lubricant, the sealing element having an elastomeric base body madeof a fluoroelastomer and a plasma coating, wherein the coating comprisesthe elements carbon, oxygen, silicon, and hydrogen, wherein the coatinghas the following properties at least at the surface: the amount ratioC:Si (at %/at %) is >5 the amount ratio O:Si (at %/at %) is >3, and thesurface energy is <50 mN/m.
 15. A method for producing the sealingelement according to claim 14 by plasma-assisted vapor deposition, themethod comprising the steps of: (a) introducing the elastomeric basebody into the plasma device, (b) introducing at least one gaseoussilicon precursor into the device, and (c) coating the base body in thedevice.
 16. The method according to claim 1, wherein the coatingcomprises the element fluorine.
 17. The method according to claim 1,wherein the coating has the following proportions (in at %) at least atthe surface: Carbon: 60% to 90% Oxygen:  9% to 18% Silicon:  1% to 4%Fluorine:  0% to 25%


18. The method according to claim 8, wherein the contact angle of thecoating relative to the lubricant is from 15° to 30°.
 19. The sealingsystem according to claim 12, further comprising a lubricant.
 20. Thesealing element according to claim 14, wherein the coating comprises theelement fluorine.